Add an option to list only feature types with geometries to jdbc-ng datastores

Atm the datastores list both geometric and non geometric tables.
This is due to a couple of good reasons:

• people might want to manipulate geometryless tables as well
• metadata necessary to recognize a table as geometric might be missing

However, the most common case is the one of people wanting to just play with geometric tables.
So, add an option to only report feature types with geometries (not sure if we want to make this option the default)